1. Field of Invention
This invention relates to a damper and, more particularly, to a damper suitably used as a shock absorber or front fork on the suspension of a bicycle, motorcycle, automobile or other vehicle.
2. Description of Related Art
Dampers (shock absorbers, MacPherson struts, front forks, etc.) for controlling vehicle body motion and handling characteristics during vehicle travel over uneven surface are well-known in the art. Dampers typically comprise a closed hydraulic cylinder with an internal piston connected to a central piston rod, which reciprocates within the cylinder to produce damping forces.
As is well known in the art, the damping forces created by a damper have a major influence on the overall dynamic performance of a vehicle. A wide range of dynamic conditions are encountered during typical vehicle motion over various surfaces and terrain features. For example, these features and conditions include large and small bumps, sharp-edged bumps and round-edged bumps, close-spaced bumps and widespaced bumps, stutter bumps and gradual undulating bumps, and so forth. In addition, conditions include vehicle acceleration and deceleration modes, uphill and downhill travel modes, as well as turning modes.
Besides the factors noted above, different operators of a specific vehicle traversing identical terrain features often prefer significantly different damping characteristics. This is especially true for light-weight vehicles, such as bicycles or motorcycles, where rider weight can be a major portion of total weight, and where rider “style” or “technique” can have a significant influence on overall suspension performance.
As a result of the wide variety of dynamic conditions and individual factors which a vehicle damper responds to, as noted above, it is desirable to provide means for adjusting damping forces to suit particular situations. As is known in the art, damping forces of many dampers can be altered by disassembling the damper and changing internal parts. Also, as is known in the art, various mechanisms have been developed over the years for quickly adjusting damping forces externally, without disassembly of the damper, for example by pre-setting an adjustable knob on the damper.
For example, Fox et al U.S. Pat. No. 6,360,857 teaches a mechanism for externally adjusting damping forces.
In addition to providing for alteration of damping forces via pre-set external adjustments, various constructions have also been taught in the damper art to provide remote adjustment, as well as dynamic, automatic modulation of damping forces based on sensing and reacting to internal or external conditions or inputs.
One example of dynamic modulation of damping forces based on sensing and reacting to internal conditions, common to most conventional dampers, is the velocity-sensitive characteristic, wherein damping forces generally increase as the velocity of the piston increases (there are, however, wide variations in the force-vs-velocity curve shapes and force levels found in various dampers calibrated for specific applications and conditions).
An example of a construction for modulating damping force based on sensing an external condition is shown in the Hein U.S. Pat. No. 2,698,068. In the Hein patent, a damper is shown which includes hydraulic communication from the vehicle braking system to a passage down the center of the piston rod which leads to a valving arrangement in the damping piston. In operation, application of the vehicle brakes acts on the compression valving to provide an “anti-dive” effect at the front of the vehicle. One drawback of this construction is that it is only capable of reacting to one specific condition, the application of the vehicle brakes.
An example of a construction for modulating damping force based on dynamically reacting to an external input is shown in the Engel U.S. Pat. No. 5,207,300. In the Engel patent, a damper is shown which includes an external pressure source input which communicates via a central passage through the piston rod to a valving arrangement in the damping piston which includes a vented pressure intensifier. In operation, variations in the pressure applied by the external source produce dynamic variations in the damping characteristics of the damper. Drawbacks of this construction include its relative complexity and cost, as well as blocked availability to the central passage down the piston rod, which could otherwise be utilized for inclusion of alternate pre-set adjustment mechanisms in communication with the damping piston.
Another example of a construction for automatically modulating damping force based on sensing and reacting to internal conditions is shown in the patent to Curnutt, U.S. Pat. No. 5,190,126.
In the Curnutt patent, a damper is shown which includes a conventional cylinder and a piston rod with an attached first piston which divides the interior of the cylinder into two chambers. Fluid flow through the first piston is controlled by an adjoining, pressure-sealed second piston which is driven by pressure differentials to move relative to the first piston. Motion of the second piston relative to the first piston blocks or unblocks flow passages in the first piston, thus creating the compression damping forces produced. One drawback of this construction is that it produces a relatively “flat” force vs. velocity compression damping curve (a “blow-off” type of damping characteristic), which can be difficult to tune for specific applications and conditions.
The present invention was developed to provide an improved damper which provides automatic modulation of damping forces based on sensing and reacting to internally-generated or externally-generated conditions, and that avoids the above and other drawbacks of the known prior art.